Miley Cyrus and Madonna appear in this photo Cyrus posted on her Instagram page just after midnight on Jan. 29, 2014, ahead of an 'MTV Unplugged' special that reports said would feature a guest appearance by the Queen of Pop. / The two are pictured in a photo shared by Madonna's manager, Guy Oseary. (instagram.com/mileycyrus / instagram.com/guyoseary)

UPDATE at 12 a.m. ET: Miley Cyrus shared on her Instagram page a photo of herself and Madonna dressed in bedazzled cowboy outfits -- a nod to the latter star's 2000 music video "Don't Tell Me." Both are sticking out their tongues -- a pose Cyrus has become known for in recent months.

Madonna's rumored collaboration with Cyrus comes on the heels of her recent performance with rapper and producing partners Macklemore & Ryan Lewis at the 56th annual Grammy Awards. The singer joined the duo on stage, following up their rendition of "Same Love" with her hit "Open Your Heart" as 33 couples were married by Queen Latifah.

Madonna, known as the Queen of Pop in the 1980s and among the first artists to push the envelope when it comes to sexually-explicit or otherwise controversial performances. Cyrus, who has stirred mixed reactions over her new image over the past year, announced her MTV "Unplugged" show on Jan. 20. Some of the most legendary artists have been featured on the special over the years, including Mariah Carey, Nirvana and Bob Dylan.